The present invention relates to an improvement in the processing of oilseeds such as, for example, soybean, cottonseed, corn, peanut, safflower, sunflower, and palm. More particularly, the invention relates to an improved process for the extraction of oils from oilseeds utilizing an isopropyl alcohol-based extraction solvent.
The oilseed industry of the United States produces on an annual basis about thirteen million tons of seed oils from roughly one billion bushels of seed crops, predominantly soybean and cottonseed. Essentially all of this oil is recovered from the seeds by multi-stage countercurrent solvent extraction. The oils find primary use in foods, e.g., shortening, margarine, cooking oils, and salad oils, while seed meal from which the oil has been extracted, having a high protein content, is generally processed into animal feeds. About two percent of this meal is further refined for human consumption.
In the recovery of seed oils, the industry consumes large quantities of extraction solvent. Hexane has long been recognized as the standard solvent in the industry, due in part to its low cost relative to other solvents and in part to its physical and chemical properties. However, in recent years incentive has developed for the replacement of hexane as the solvent of choice for oilseed extraction. Increasing hexane costs and possibilities of supply shortages account for some of this incentive. In addition, for health and safety reasons, solvent specifications in the industry, precautions to prevent exposure of workers to hexane, and relevant hydrocarbon emission standards may be tightened. Furthermore, interest in producing an upgraded seed meal, for instance a meal suitable for human consumption without the need for secondary extraction or other refining, has given rise to attempts at use of alternate extraction solvents.
Of particular relevance to the present invention is the prior art relating to extraction of oilseeds with an isopropanol-based solvent. Characteristics of isopropanol extraction are generally well known and are described, for instance, by Harris et al in a three-part publication entitled "Isopropanol as a Solvent for Extraction of Cottonseed Oil" (J. Am. Oil. Chem. Soc., November 1947, Vol. 24, p. 370-375; December 1949, Vol 26, p. 719-723; and July 1950, Vol. 27, p. 273-275). More recent developments in oilseed processing with isopropanol are outlined by Youn and Wilpers in U.S. Pat. No. 4,298,540.
It is recognized that, although isopropanol is in many respects attractive for use as an oilseed extractant, it cannot as a practical matter be directly substituted in a process designed for use of a hexane solvent. Direct substitution would, for example, entail substantial increases in process energy requirements. Under conventional hexane extraction processing, solvent (e.g., for recycle) is recovered from both the oil and meal products by evaporation. However, because energy necessary for this evaporation is a major factor in processing costs, because the heat of vaporization of an isopropanol-water azeotrope is nearly three times that of hexane, and because isopropanol extraction typically requires greater quantities of solvent than hexane extraction, it is not economically feasible to practice a like evaporation of isopropanol-based solvent. The above-referenced publications of Harris et al describe a method for cooling and phase separating solvent and extracted oil in the process extract, or miscella as it is known in the art, which has advantages in energy conservation over evaporative separation.
It is an object of this invention to enhance the efficiency of seedoil recovery in an oilseed extraction process utilizing an isopropanol-based solvent, particularly a process in which miscella is cooled and phase separated to obtain oil-rich and solvent-rich streams.